* Re: [PATCH] serial: 8250: Return early in .start_tx() if there are no chars to send [not found] <20220217211839.443039-1-u.kleine-koenig@pengutronix.de> @ 2022-04-07 13:27 ` Tony Lindgren 2022-04-11 9:56 ` Tony Lindgren 0 siblings, 1 reply; 2+ messages in thread From: Tony Lindgren @ 2022-04-07 13:27 UTC (permalink / raw) To: Uwe Kleine-König Cc: Greg Kroah-Hartman, Jiri Slaby, Johan Hovold, linux-serial, kernel, Steffen Trumtrar, linux-arm-kernel, linux-omap, regressions Hi, * Uwe Kleine-König <u.kleine-koenig@pengutronix.de> [700101 02:00]: > From: Steffen Trumtrar <s.trumtrar@pengutronix.de> > > Don't start the whole chain for TX if there is no data to send. This is > mostly relevant for rs485 mode as there might be rts-before-send and > rts-after-send delays involved. > > Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> > --- > Hello, > > a few other drivers have such an early exit already (imx, stm32-usart). > I wonder if it applies to all UART drivers that there is nothing to do > in .start_tx() if the circ buffer is empty and there is no x_char to > send. In this case it would be more sensible to ensure in serial_core > that .start_tx() is only ever called if there is something to do. This patch seems to cause a runtime PM regression in v5.18-rc1 where 8250 is never idled for omaps. Looks like the return added here is not paired with put for the serial8250_rpm_get_tx() call above? Regards, Tony #regzbot ^introduced 932d596378b0 > drivers/tty/serial/8250/8250_port.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c > index 3b12bfc1ed67..5d4668f12f71 100644 > --- a/drivers/tty/serial/8250/8250_port.c > +++ b/drivers/tty/serial/8250/8250_port.c > @@ -1657,6 +1657,9 @@ static void serial8250_start_tx(struct uart_port *port) > > serial8250_rpm_get_tx(up); > > + if (!port->x_char && uart_circ_empty(&port->state->xmit)) > + return; > + > if (em485 && > em485->active_timer == &em485->start_tx_timer) > return; > > base-commit: 754e0b0e35608ed5206d6a67a791563c631cec07 > -- > 2.34.1 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] serial: 8250: Return early in .start_tx() if there are no chars to send 2022-04-07 13:27 ` [PATCH] serial: 8250: Return early in .start_tx() if there are no chars to send Tony Lindgren @ 2022-04-11 9:56 ` Tony Lindgren 0 siblings, 0 replies; 2+ messages in thread From: Tony Lindgren @ 2022-04-11 9:56 UTC (permalink / raw) To: Uwe Kleine-König Cc: Greg Kroah-Hartman, Jiri Slaby, Johan Hovold, linux-serial, kernel, Steffen Trumtrar, linux-arm-kernel, linux-omap, regressions * Tony Lindgren <tony@atomide.com> [220407 13:25]: > Hi, > > * Uwe Kleine-König <u.kleine-koenig@pengutronix.de> [700101 02:00]: > > From: Steffen Trumtrar <s.trumtrar@pengutronix.de> > > > > Don't start the whole chain for TX if there is no data to send. This is > > mostly relevant for rs485 mode as there might be rts-before-send and > > rts-after-send delays involved. > > > > Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de> > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> > > --- > > Hello, > > > > a few other drivers have such an early exit already (imx, stm32-usart). > > I wonder if it applies to all UART drivers that there is nothing to do > > in .start_tx() if the circ buffer is empty and there is no x_char to > > send. In this case it would be more sensible to ensure in serial_core > > that .start_tx() is only ever called if there is something to do. > > This patch seems to cause a runtime PM regression in v5.18-rc1 where > 8250 is never idled for omaps. > > Looks like the return added here is not paired with put for the > serial8250_rpm_get_tx() call above? FYI I just posted two fixes for these early return cases: https://lore.kernel.org/linux-serial/20220411094805.45696-1-tony@atomide.com/T/#t Regards, Tony _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2022-04-11 10:28 UTC | newest] Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <20220217211839.443039-1-u.kleine-koenig@pengutronix.de> 2022-04-07 13:27 ` [PATCH] serial: 8250: Return early in .start_tx() if there are no chars to send Tony Lindgren 2022-04-11 9:56 ` Tony Lindgren
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